Polymeric surfactants are known for use in stabilising oil water interfaces, particularly in water-in-oil emulsions, oil-in water emulsions and dispersions. Such surfactants include A-B-A block co-polymeric surfactants in which the A blocks are polyester blocks, particularly polyesters of hydroxyl aliphatic acid for example of hydroxystearic acid to give polyhydroxy stearate (PHS) blocks, and the B block is a polyalkylene glycol block, especially a polyethylene glycol (PEG) block. Such polymeric block surfactants are described in EP 0000424 A and their use in stabilising the emulsion used in inverse emulsion acrylamide polymerisation in GB 2157744 and U.S. Pat. No. 4,776,966. The molecules of these surfactants have a shape that makes them particularly useful in stabilising water-in-oil dispersions and emulsions. It is believed that, at the oil/water interface, the molecule sits with the hydrophilic PEG block in the water phase and the two hydrophobic PHS blocks in the oil phase. This arrangement gives good packing at the interface and is believed to contribute to the effectiveness of these materials. These surfactants have been used in industrial applications. More recently these surfactants have been used in personal care applications to stabilise water-in-oil dispersions and emulsions when the manufacturing process was changed so that xylene was not used as a solvent. The possible presence of residual xylene in the final product surfactant had previously precluded the use of the surfactants in skin contact applications. For example WO 98/55088 describes a personal care composition which is or includes a hydrophile-in-oil emulsion or dispersion which includes as a dispersant and/or emulsifying agent a block copolymeric surfactant of the formula A-B-A.
For many of the above industrial and personal care applications the molecular weight of the PEG block needs to be higher than 1000. In such cases the polymeric surfactant is typically a waxy solid. Whilst the waxy solid is a very effective emulsifier and/or dispersant, liquid polymeric surfactants having the same properties would be more desirable. Such liquid polymeric surfactants would be easier to handle and process. Cold processing is advantageous for volatile and/or heat sensitive ingredients in personal care formulations, for example perfumes. Furthermore cold processing is easier to undertake, more economical and energy efficient.
Typically the A block of the A-B-A polymeric surfactant is the residue of PHS which has been chain terminated with stearic acid. We have now surprisingly discovered new polymeric surfactants derived from star polymers which are liquid and are effective emulsifiers and/or dispersants.